The present invention relates to methods, systems and apparatus for terminated call control for roaming cellular telephony.
Systems for supporting mobile telephones when they are outside their home network geographical areas, a phenomenon known as roaming, are well known. Generally a mobile telephone moves within the geographical area of its home network, typically a country, and within that country it moves around different base stations and local visitor location registers (VLRs). When the telephone is outside the geographical region of the network, then it connects to a foreign network, and registers at a roaming VLR. The VLR checks for the corresponding home location register (HLR) to verify the telephone and then allows calls to proceed. The HLR makes a note of the currently responding VLR so that any calls to the telephone can be routed from the HLR to the VLR and the call can be completed.
One phenomenon that occurs with International calls to roamers occurs with call forwarding to mailboxes or to other numbers and is known as tromboning. The calling party calls the roamer who does not answer. The unsuccessful caller is then forwarded from the roamer to the roamer's mailbox where he leaves a message. At this point the calling party is connected via an outgoing international leg to the roamer and then via a second incoming international leg back to the roamer's home network where his voicemail is located. When this happens the calling party pays for a local call, since he dialed a local number. The called party however has to pay for two international legs of the call, all this for a call that he did not even answer. The phenomenon is known as tromboning, and leads to substantial ill feeling and customer care issues with subscribers, so much so that many are induced not to use roaming at all, or at least to cancel their mailboxes whilst roaming, leading to substantial loss of opportunity for further calls.
An additional issue with roaming is that telephone numbers or caller identifications are often lost over international lines, so that the calling number does not appear on the roamer's screen, preventing him from carrying out his own call screening and preventing him from returning calls he was unable to answer.
In more detail, Mobile subscribers normally set call forwarding instructions to the voicemail. Late Call Forwarding is performed conditionally due to the subscriber's inability to answer a call routed to the handset. Conversely, Early Call Forwarding is performed without the network's attempt to route the call to the handset. This happens when the handset is shut off or when the subscriber requests unconditional forwarding of all incoming calls. Late Call Forwarding for busy/no-answer/not-reachable conditions can be configured to any number, usually to the subscriber's voice mailbox.
Mobile subscribers roaming abroad want to stay in touch with work and home, and continue to use their mobile services, such as voicemail. They also naturally want the same user experience as in the home network—such as seamless caller access to mailbox, caller-ID indication in retrieval and direct forwarding of calls to their voice mailbox or to any of their pre-set forwarding destinations.
However, when a roamer cannot take a call—either unavailable, busy or chooses not to answer—the visited network routes the call back to the home voicemail system (the default setting for most roamers). This in turn causes inefficient international tromboning, resulting in a negative impact on the caller and subscriber experience, and forces roamers to pay international tariffs for voicemail deposits.